Road haulage is playing an ever increasing role in North American transportation, with heavy reliance being placed upon large trucks and truck-trailers, used in long distance hauling. In some jurisdictions the vehicle weight and size limitations have been extended, presumably beyond the design limits of the existing vehicle components. As a consequence there have been a large number of wheel break-free occurrences, many of which have resulted in fatalities, with runaway wheels impacting other vehicles.
The approximate weight of 470 pounds (lbs) of a truck wheel and its tire, allied to typical highway speeds of, and sometimes well in excess, of 60 miles an hour (mph), i.e. 100 km/hr, result at wheel breakaway in an energy scenario both strange and deadly. It has been observed that frequently upon breakaway under these conditions the released wheel accelerates past the parent vehicle. Apparently due to its conditions of release, any tendency to bounce becomes exagerated, such that succeeding bounces are excessively higher, so that bounces as high as fifty feet have been reported. Impact under such conditions is extremely destructive.
Without any such bouncing, collision with such an object at joining speeds usually in excess of 120 mph has proved to be almost invariably fatal.
Improved maintenance and safety checks do not appear to have the answer to this problem, which appears to be primarily the consequence of component overloading, particularly wheel bolts, and possibly axle components.